Gas ejector with built-in sound attenuating means



Sept. 23, 1969 A. VEGEBY 3,468,397

GAS EJ'ECTOR WITH BUILT-IN SOUND ATTENUATING MEANS Filed Oct. 24, 1967 mvzmon: ANDERS VEGEBY WWZW ATTYS.

United States Patent 3,468,397 GAS EJECTOR WITH BUILT-IN SOUND ATTENUATIN G MEANS Anders Vegeby, Bandhagen, Sweden, assignor to Aktiebolaget Svenska Flaktfabriken, Stockholm, Sweden Filed Oct. 24, 1967, Ser. No. 677,597 Claims priority, application Sweden, Oct. 26, 1966, 14,707/ 66 Int. Cl. F0111 3/06 US. Cl. 181-36 5 Claims ABSTRACT OF THE DISCLOSURE A sound attenuator for an ejector using high-pressure gaseous medium from an outflow nozzle comprising a substantially cylindrical tube surrounding the nozzle and having an external lining of sound absorbing material, the tube being at least partially perforated. The external lining of the tube is enclosed in a casing of perforated metal and the tube extends from the inlet throat of the ejector rearwardly around the nozzle. The tube may terminate immediately beyond the nozzle, may be extended substantially therebeyond, or may project outside of the ejector and communicate with the surrounding atmosphere.

This invention relates to an ejector for transporting gases by utilizing steam or another gaseous medium of a relatively high pressure as driving medium, which ejector comprises an inlet portion connected to the gas conduit in question, a mixing portion with a softly rounded inlet, a ditfusor-shaped outlet portion and a supply line for the driving medium provided with an outflow nozzle opening into the ejector.

In process as well as ventilation technology normally fans are employed for the industrial transport of gases. If the gas to be transported has a high temperature, the fans require in many cases very much space, because the volume of the gas increases with rising temperature and the specific weight of the gas decreases, whereby the available pressure head of a certain given fan is lowered. Moreover, regard must be paid to pressure losses and possible pressure recovery, when the ducts are mounted before and after the fan, which in .many cases can increase the space requirement for a fan to a substantial degree.

In view of the space requirement, therefore, it was considered in several cases more suitable to use an ejector instead of a fan. Usually the ejector can be arranged as a part in a straight gas duct and, thus, requires only little space.

The ejector can be given smaller dimensions, when a drive medium with high speed is used, for example steam with a pressure of 3 at g or higher. In certain cases it can be necessary, in view of the space requirement, to apply very high steam pressures, for example directly from a boiler with a pressure of 50 at g or higher.

The efliciency degree of an ejector is lower than that of a fan, but this difference can be compensated for in many cases by the diflerences in costs for the different types of energy carriers utilized, in this case electricity, and the kinetic energy of the steam. When the fan or the ejector is utilized only for a short period of the year, the operation costs can be disregarded compared with the initial capital expenditure. The latter is lower for the ejector, in many cases only a fraction of that of the fan, particularly if the fan requires the building volume to be increased, which is the case with so-called starting ejectors versus corresponding fans for soda recovery units in the cellulose industry.

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The fan as well as the ejector involve the inconvenience of producing noise, which in the case of free exhaust can be annoying and irritating for the environment. In such cases it is desired to attenuate the sound level by suitable inserts, in which connection it appears to be most near at hand to attach the sound attenuating material around the ejector or fan and after the same, when the exhaust is made directly into the environment or the sound is conveyed with the transported gas in the duct after the ejector or fan. In many cases corresponding arrangements must be made also on the inlet side. This involves normally no difliculties, if the transported gas is free of dust-like impurities.

If the transported gas includes dust, and particularly if the dust is hygroscopic, so that in the deposited dust moisture easily is absorbed, the sount attenuating inserts, which usually are made of a porous material, can get clogged. This is especially the case, when the plant is operated discontinuously, so that it is cooled between the operation periods. The risk of clogging after the ejector 1 is very great, particularly in cases where the ejector is driven with steam, which, as mentioned above, ofiers advantages with respect to the initial capital expenditure. Said clogging has its reason in that the partial pressure of the water vapour, especially at the start, is high in relation to the saturation pressure, which results in condensation during the heating-up period after the start from cold temperature. Upon condensation in the sound attenuatingmaterial the risk of the formation of dust coatings is increased considerably. These coats harden in many cases, subsequent to the drying after the ejector has reached operation temperature, so that after a short time the sound attenuating portion is fllled with hardened dust and has no eifect at all.

Also for entirely pure gases, which, however, contain condensable vapours, it is diflicult to provide sound attenuating with the porous materials normally used, because these materials have a certain heat-insulating effect. Hereby that portion of the gas duct or ejector, which usually is the last portion of the diifusor, where the sound attenuating material is attached, will be cooled from the environment, and in most cases the material will be damaged by corrosion.

The aforesaid diificulties and inconveniences are overcome by the invention, which is characterized in that concentrically around the outflow nozzle for the drive medium there is mounted a substantially cylindric tube with a lining of sound absorbing material on its outside and acting as a sound trap and primary ejector. Due to this construction the material in the sound attenuating portion is heated very rapidly so that the risk of condensation is eliminated, and as it is placed in the gas flow, condensation from the environment will not occur, either.

The invention is described in a greater detail with reference to the accompanying drawing, in which FIGS. 1, 2 and 3 are longitudinal sections through different embodiments of the invention.

In the drawing, 1 designates an ejector comprising an inlet portion 2 adapted to be connected to a gas conduit (not shown), a mixing portion 3, a diifusor-shaped outflow portion 4 and a supply line 5 for the drive medium. The mixing portion 3 is provided in known manner with a softly rounded inlet 3a, and the supply line is equipped with an outflow nozzle 6, which in the illustrated embodiments is shaped like a so-called Laval nozzle.

According to the first invention, concentrically around the outflow nozzle 6 there is mounted a substantially cylindric tube 7 provided on its outside with a lining 8 of sound absorbing material. The tube with the associated lining acts as a sound trap and attenuates the annoying sound, which substantially is produced by the drive medium jet prior to its braking by means admixed with the gas being transported. As the sound also spreads backwardly in relation to the direction of the drive medium jet, it may be suitable to add an extension to the sound trap as designated with broken lines at 7a in FIG. 1. The tube 7 may be perforated entirely or partially, and to the outside of its lining of sound absorbing material is attached an outer casing 9 of perforated sheet metal.

In certain cases it may be motivated to design a tube 17 as a complete ejector with inlet portion, mixing portion 15 and diftusor 16, as it appears from the embodiment of the inventionshown in FIG. 2. In this embodiment the outflow portion 16 of the tube 17 is provided with a contracted outflow opening 10. The tube 17 is imperforate in the mixing portion 15, and the outer lining 18 is enclosed in a perforated casing 19.

In certain cases it may be suitable to apply a gas other than the gas transported, for example air, as a complementary drive medium. In that case the sound trap, which acts as primary ejector, is mounted so, as appears from FIG. 3, that its inlet end communicates directly with the surrounding atmosphere. The outer lining 28 is a casing 29 which is perforated only in the area within the inlet portion of the ejector.

The three drawing figures show the solution in principle for diflerent embodiments of the invention, but the constructional design of the details comprised therein can, of course, be varied in several ways without departing from the idea of the invention.

I glaim:

1. Ejector for the transport of gases from a conduit by using a gaseous medium of a relatively high pressure as drive medium, said ejector comprising an inlet portion connected to the gas conduit, a mixing portion with a softly rounded inlet, a diffuser-shaped outflow portion and a supply line for the drive medium provided with an outflow nozzle opening into the ejector, characterized in that concentrically around the outflow nozzle for the drive medium there is mounted a substantially cylindric tube provided on its outside with a lining of sound absorbing material and acting as a sound trap and primary ejector.

2. An ejector according to claim 1, characterized in that the tube acting as sound trap is at least partially perforated.

3. An ejector according to claim 1, characterized in that the sound absorbing material on the outside of the tube is provided with an outer casing of perforated sheet metal.

4. An ejector according to claim 1, characterized in that the tube acting as sound trap is constructed as a complete ejector, provided with a contracted outflow opening.

5. An ejector according to claim 1, characterized in that the tube acting as sound trap communicates at its inlet end directly with the surrounding atmosphere.

References Cited UNITED STATES PATENTS 1,473,037 11/ 1923 Greig 230-92 2,857,332 10/1958 Tenney et al. 2,969,748 I/ 1961 Staats et al. 230-92 XR 3,061,179 10/1962 Pendleton 230232 XR ROBERT S. WARD, 111., Primary Examiner U.S. Cl. X.R. 230-92, 233 

